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7182Re: Colour coding on the aberration graph

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  • Craig Stark
    Jan 23, 2006
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      OK, so here is what I believe it means. I am no expert, but I did
      look into this a bit some time ago. FWIW, this page may help explain
      the issues:
      http://www.vanwalree.com/optics/chromatic.html

      The "Longitudinal Aberration" is showing the distance between focal
      planes for light of varying wavelengths. Red light focuses in a
      different place that blue light. As we visually focus on green (where
      we are most sensitive), the shift in focal planes for different freqs
      of light "blur" those freqs and lead to things like color halos.

      So, what this graph is showing is for different frequencies (I think
      we can safely ignore the 435 and 707nm) how far off focus are we? If
      we find the spot where they cluster the most (about the third tick
      from the top) and say that we have our focuser at this position
      (y-axis here is focal plane position), we can see that we have a nice
      clustering. Ignore the dark blue and the dark red (getting pretty UV
      and IR) and the focal plane shift for a nice cluster in there save the
      ~656 (Ha-like line) is on the order of .05mm.

      Craig
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